This invention relates generally to signal measurement and more particularly to the measurement of the phase difference between a known reference signal and a signal to be measured.
Many prior art devices have been developed to perform measurements of the type made by this invention. A typical known circuit is disclosed in U.S. Pat. No. 3,591,854 to Cole, but the prior art has evidenced several operational deficiencies. For example, the Cole disclosure teaches the use of a circuit employing grounded capacitors. This configuration results in erroneous indications of phase measurement unless the time constants of both legs of the circuit are equal. Various harmonic components contained in the signals to be measured can also produce an error because the capacitors are grounded. Circuits configured as in Cole further require the use of carefully matched resistors and capacitors to achieve the symmetry necessary for accurate phase measurement. Further, the use of the zero crossing detector in conjunction with an adjustable impedance that works in association with the operational amplifier provides a particularly stable and accurate phase measurement system.